The objective of the Checklist Validation of Dietary Questionnaire Study is to compare the validity of a newly developed food frequency questionnaire, the NCI Diet History Questionnaire (DHQ) with the validity of a more standard food frequency questionnaire, the Block Health Habits and History Questionnaire (HHHQ). Each participant will report food intake every day for 30 days on the Daily Checklist, a criterion reference instrument, which he or she will complete and mail each day. At the end of the 3-day period, each participant will estimate his or her intake for the last month using either the DHQ or the HHHQ. Validity will be measured as agreement between the frequency of intake estimates from each questionnaire, and the frequency of intake estimates from the daily checklists. Results from this experiment will be used to refine the final design of the DHQ, which will then be available to researchers at NTH and the extramural community. Improvements in dietary assessment will lead to more precise estimates of intake and thus an enhanced ability to detect diet and disease relationships.